Organic food is no healthier than food grown through conventional methods, according to a group of scientists at Stanford University. After examining the results of 237 past studies on the subject, they concluded that fruits, vegetables and meat labeled organic had, on average, the same nutritional value as their cheaper, nonorganic counterparts.
The surprising finding may have some people reassessing which shelf to shop from at the supermarket, but supporters of the organic movement say there are still many reasons to shell out extra cash for organic groceries. If so, what are they?
Some consumers shy away from conventionally grown produce to avoid residues of the synthetic chemicals that get sprayed onto crops to kill pests on conventional farms. Organic farms are generally pesticide-free, relying on natural pest-control methods to keep bugs at bay. Indeed, the Stanford research found that 38 percent of conventionally grown food samples contained traces of pesticides.
These pesticide residues can have hidden health consequences. According to the New York Times, three studies published last year found that pregnant women who are exposed to higher amounts of pesticides known as organophosphates end up having children with IQs that are several points lower, on average, than those of their peers.
However, there's a twist. The Stanford scientists found that 7 percent of the organic food samples in the studies they examined contained traces of pesticides as well, despite the fact that organic farms should be pesticide-free. "This may be due to pesticide drift, persistent pesticides in the soil from previous conventional farming, storage or harvesting practices resulting in contamination, or mislabeling," study co-author Dr. Crystal Smith-Spangler wrote in an email. The possibility of pesticide contamination of food across the board suggests people should wash both organic and nonorganic produce before eating it. And washing the food erases the difference between the pesticide levels that existed, said Dr. Dena Bravata, lead researcher and a health policy affiliate at Stanford School of Medicine.
But the argument for less contamination is stronger when it comes to organic animal products, she said. Whereas animals raised on conventional factory farms are typically treated with antibiotics to prevent the infections that would otherwise plague livestock living in such close quarters, organic meat and dairy are antibiotic-free. Similarly, some conventional dairy farms inject cows with artificial growth hormones, while organic dairy farms do not. This means consumers of organic animal products can avoid contributing to the development of antibiotic-resistant bacteria, and they can steer clear of any potentially adverse effects of consuming hormones (although such effects have not been clearly identified). [Will People Really Be Forced to Stop Eating Meat?]
In surveys, people who buy organic food report doing so in part because they prefer the taste. However, Bravata said taste differences between organic and conventional food have not been substantiated in the lab. Are taste advantages just another widely held misconception? Perhaps, but taste advantages could also result from the fact that many organic farms tend to get food to consumers more quickly than conventional farms, a factor that strongly affects taste.
Studies show fresh, ripe fruit and vegetables taste better. "That has nothing to do with whether it was grown organically or not, but everything to do with harvest, storage, and how long it takes to get the food from farm to table," Bravata said. Some of the places one tends to find organic produce, such as farmers' markets and farm-to-table restaurants, will use local, and thus more recently harvested, produce, and so it tastes better, she said. [Organic vs. Local: Which Food Is Best?]
For many consumers, the choice to go organic stems from environmental concerns. Not only do the chemical fertilizers and pesticides applied to conventional farms require fossil fuels to produce, scientists say they also have negative consequences for the Earth. But what are these consequences?
On conventional farms, the nitrogen, phosphorus and potassium plants need to grow are added to the soil in chemical form each season, and, according to David Pimentel, an emeritus professor of ecology and agriculture at Cornell University, each season, excess fertilizers leach into the water.
"The runoff of unutilized synthetic nitrogen fertilizer from conventional agriculture into both ground and surface waters and the atmosphere — where, as nitric oxides, it contributes to global climate change as a greenhouse gas – is a major problem in the U.S. and elsewhere," Pimentel told Life's Little Mysteries. "The 'dead zones' in the Gulf of Mexico are due to nitrogen fertilizer runoff from fields in the Corn Belt and elsewhere that stimulate phytoplankton blooms and die-offs, which then decay and deplete the water column of oxygen."
Organic farms, by comparison, provide the nutrients needed for crop growth by enriching the soil with compost, manure and by planting "cover crops" in fields between each growing season, Pimentel explained. Cover crops, which often include legumes, not only physically protect fields from erosion, they also are associated with bacteria that can convert atmospheric nitrogen into a form plants can use, and they increase the soil's content of organic matter, which functions to increase its water- and nutrient-holding capacity.
"Preventing soil erosion eliminates much of the need for synthetic fertilizers," Pimentel said, "since eroded soil includes a disproportionate amount of soil organic matter to which nitrogen, phosphorus and potassium tend to be adsorbed onto, and the soil left with less soil organic matter is even more erodible. Conventional continuous monoculture of crops simply is not sustainable."
For those who argue that conventional farming is simply a necessary evil for feeding the outsized human population — and so, the question is often asked, why spend more at the supermarket to prop up a doomed agricultural model? — this belief appears to be outdated.
According to Pimentel, farms wildly overuse chemicals. In a long-term study that culminated in a paper published in 2005 in the journal Bioscience, he and colleagues were able to grow corn and soybean crops over a 22-year period "without using a drop of pesticide," he said, and the crops achieved equivalent yields to those of a conventional farm used as a control, while requiring the input of about 30 percent less fossil fuel energy.
"Commercial fertilizers for the conventional system were produced employing fossil energy, whereas the nitrogen nutrients for the organic systems were obtained from legumes or cattle manure, or both. The intensive reliance on fossil fuel energy in the conventional corn production system is why that system requires more overall energy inputs than do organic production systems," the researchers wrote.
Many countries have drastically lessened their reliance on pesticides. "Sweden has been able to reduce pesticide use over a 10-year period by 68 percent and still get the same crop yields and the same cosmetic standards," Pimentel said. The U.S. lags behind.
So, should you go organic? On the con side, organic food costs more. According to the Stanford scientists, it has roughly the same nutritional value as conventional produce, and, at least in supermarkets, isn't guaranteed to taste much better than the food on the next shelf over. On the pro side, organic food is less contaminated by hormones and pesticides, and it engenders far less unnecessary contamination of the planet with those chemicals. Ultimately, it's your call.
This articles was provided by Life's Little Mysteries, a partner site to LiveScience. Follow Natalie Wolchover on Twitter @nattyover or Life's Little Mysteries @llmysteries. We're also on Facebook & Google+.